It is common practice for cordless telephone systems to employ analog circuitry to measure the radio frequency (RF) field strength of a carrier on a receive channel, and to provide an indicative signal on a carrier detect output pin. If the signal strength is above a preset threshold level, then a signal of an appropriate logic level is developed at the carrier detect output pin. The carrier detect output pin typically is coupled to an input of a microprocessor, which reads the logic level periodically.
There are several uses for the information gathered from the carrier detect signal. For example, a microprocessor in a base unit can use this information to determine whether the handunit is out-of-range, or not. Alternatively, a microprocessor in either a base unit or a handunit can use this information to determine if a specific channel is occupied.
Unfortunately, during the manufacturing process, an adjustment procedure must be performed on the analog carrier detect circuitry in order to ensure correct triggering at the specified thresholds. This adjustment procedure tends to be difficult, time consuming, and often causes the detection of the RF carrier to be unreliable.